n. Pyogenic Cocci : The Gram’s positive Cocci : 1- Staphylococci : 2- Streptococcus : Staphylococci : is a Gram positive Cocci , one micrometer in diameter, arranged in clusters, non spore formers, and non-motile. Staphylococcus aureus species are capsulated. n.
Pyogenic Cocci: The Gram’s positive Cocci:
is a Gram positive Cocci, one micrometer in diameter, arranged in clusters, non spore formers, and non-motile.
species are capsulated.
Staphylococcus species are facultative anaerobic bacteria.
All species grow best on nutrient agar and blood agar.
Mannitol salt agar is a selective media for Staphylococcus species.
It can grow at a temperature range of 15-45 C, and NaCl concentration as high as 15%.
Clinical significance of Staphylococcus aureus:
1-Localized skin infections.
5-Food poisoning:(foodborne intoxication).
Gram positive cocci,occur in pairs and in short chains.
None-motile, none- spore formers, some strains are capsulated.
Strict anaerobes and facultative anaerobes.
Classification of Streptococcus species:
Streptococcus species are classified according to hemolytic activity.
Beta-Hemolytic: Alpha Hemolytic
Streptococcus pyogenesStreptococcus pneumoniae
Clinical significance of Streptococcus pyogenes:
1-Acute pharyngitis and tonsilitis.
2-Impetigo and deep skin
3- Acute Rheumatic fever.
Due to the bacteria M protein.
Due to antibodies interaction with glomerulus.
The Gram negative Diplococci:
Gram negative cocci , Kidney-shaped, occur in pairs, in clinical specimens: present inside the polymorphonuclear cells.
They grow best on Thayer-Martin Medium; Chocolate agar supplemented by vancomycin and nystatin.
Both factor X and V (hemoglobin, NAD) are required for Neisseria species cultivation.
A 5-10 % CO2 is required for primary cultivation.
On Chocolate agar.
1-Urinary tract infection: (Most common):
A- Gonococcal Urethritis.
B- Pelvic inflammatory disease
Gram positive Bacilli
The Gram’s positive spore former aerobic bacilli:
The genus Bacillus:
Gram-positive spore-forming, non-motile, bacilli arranged in chains.
Bacillus anthracis species are capsulated in tissue and spore-former
in the culture.
Gram’s stain smear Malachite green spore stain.
Bacillus anthracis grows on nutrient agar or blood agar in presence of oxygen (obligate aerobic bacteria).
On the blood agar, Bacillus anthraciscolonies are non-hemolytic,with irregular border.
Growth of Bacillus cereus
Bacillus anthracis :
Spore germination in skin,
a papule development,
converted into malignant
2-Pulmonary anthrax :
Enterotoxins cause food poisoning.
The Gram positive spore-forming anaerobic bacilli:
The genus Clostridium:
Gram-positive spore-forming, anaerobic large bacilli.
Clostridium tetani species forms terminal spores, while sub-terminal or central oval spores are produced by Clostridium perfringens.
All Clostridium species are obligatory anaerobic.
On blood agar, Clostridium perfringensspecies produce zone of complete hemolysissurrounded by wider zone of incomplete hemolysis.
Clostridium tetani colonies show beta hemolytic activity.
1-Myonecrosis (gas gangrene):
Caused by alpha toxin which damages host and blood cells.
2-Food poisoning: caused by Enterotoxin.
Clostridium botulinum :
Food poisoning, lead to progressive striated muscle paralysis .
-Tetanus :General muscle paralysis.
-Diarrhea, and pseudomembranous colitis due to long-term
The Non-spore former acid-fast Bacilli:
The genus Mycobacterium:
The Mycobacteriaare acid-fast, non-motile, non-spore forming rods.
The microbe can not be stained well by Gram’s stain due to the presence of waxy capsule.
Mycobacterium isbest demonstrated by Ziehl -Neelsenstaining technique; the microbes appear as thin pink rods arranged singly or in groups.
Once stained, they resist decolorizationwith 2% H2SO4and
95%alcohol (Acid-fast, Alcohol fast).
Mycobacteriumis strict aerobic, grows very slowly (2-4 weeks) on Lowenstein-Jensen medium; produce dry creamy colored colonies.
Culture characteristics of Tubercle bacillion Lowenstein Jensen medium .
The Non-spore Non-acid fast bacilli: The genus Corynebacterium:
Gram positive pleomorphic long rods with swollen one end (club-shaped).
They lie in small groups joined at angles to each other giving characteristic Chinese-letter arrangement
Corynebacterium bacilli arranged
Note the metachromatic
Aerobe or facultative anaerobe; grows rapidly on Löffler's medium at 37 C giving opaque white colonies within 4-12 hours.
On blood tellurite;
the organism reduces
Clinical significance of Corynebacterium:
1-Upper respiratory tract: Diphtheria.
Pseudo-membrane appearance. Marked lymph node enlargement. 2-Skin infection.
Diphtheria skin lesion.
Gram’s negative Bacilli
U Shaped bacilli
General properties of Enterobacteriaceae:
1- Short rods, and non-spore formers.
2- All are motile (by peritichousflagellae) except
3- Aerobes or facultative anaerobes.
4- Oxidase negative and catalase positive.
5- All ferment glucose with acid or acid and gas production
and reduce nitrate to nitrite.
Based on lactose fermentation, Enterobacteriaceae species are divided into:
1-Lactose fermenters as: Escherichia coli, Klebsiella
2-Non-lactose fermenters as: Salmonella, Shigella.
Clinical significance of some Enterobacteriaceae species:
Urinary tract infection.
Lower respiratory tract infection.
Urinary tract infection.
Typhoid fever, and food poisoning.
Vibrios are gram-negative aerobic comma shaped curved bacilli, motile with a single polar flagellum.
Vibrio choleraeserogroups O1 and O139 are responsible of
They grow on different media at high pH (8.5-9.5) as alkaline peptone water and TCBS.
Curved S, U-shaped bacilli:
The Genus Helicobacter andCampylobacter :
-Gram’s negative pleomorphic S or U-shaped Bacilli.
-Fastidious microbe grow best on Enriched media
supplemented by Bovine serum albumin and antibiotics
-Microaerophilicbacterium(5% O2, 10% CO2)
peptic ulcer disease.
The Genus Brucella:
Gram-negative non-motile, non-capsulated short coccobacilli.
Aerobic bacteria; grow best on liver extract agar at 5-10%
Brucella melitensis: Malta fever.
It is mainly a pathogen of goats and sheep.
It the strain found in the Mediterranean area and Arabian
Brucella abortus:Malta fever.
infects cattle mainly but can infect other animals.
-Ithas a characteristic helical shape, tightly coiled bacilli like a
-All are Gram’snegativespiral bacilli with endoflagella
-Because it can not be stained by Gram’s stain;
wet-mount Preparation should be examined by Darkfield-
-Primary, secondary, and
late stage Syphilis.